A family of alpha-amino acid salicylaldiminates incorporating the binuclear V2O33+ core: Electrosynthesis, structure, and metal valence

The green title complexes of the type Et(4)N[V2O3(L-Asal)(2)] have been synthesized in nearly quantitative yields by one-electron electroreduction (at 0.2 V vs SCE) of V2O3(L-Asal)(2) in dichloromethane solution containing tetraethylammonium perchlorate. Here L-Asal(2-) is the deprotonated salicylaldimine of L-alanine (A = al), L-valine (A = va), or L-phenylalanine (A = pa). Electronic and IR spectra as well as metal reduction potentials (E(1/2) similar to 0.4 V vs SCE) of the complexes are reported. In Et(4)N[V2O3(L-alsal)(2)]. MeCN both the metal atoms have distorted square pyramidal geometry but the metrical differences between the two are considerable. The relative disposition of the two terminal V = O groups in the complex is intermediate between cis and trans. The V-O-V angle and V ... V distance are 113.2(3)degrees and 3.067(3) Angstrom, respectively. The two V-O lengths in the V-O-V bridge are very unequal, 1.768(6) and 1.905(7) Angstrom, corresponding to a V-V-O-V-IV description. Valence localization is consistent with the V-51 hyperfine structure of the axial EPR spectra (3d(xy)(1) ground state) of the whole family of solid complexes: s = 1/2; g(parallel to) similar to 1.95, g(perpendicular to) similar to 1.98, A(parallel to) similar to 180 G, and A(perpendicular to) similar to 67 G at 300 K. The spectra in frozen (77 K) dichloromethane solution are essentially the same. On the other hand, isotropic room temperature solution spectra of the family have 15 hyperfine lines (g(iso) similar to 1.97; A(iso) similar to 51 G) revealing that the unpaired electron and hence the metal valence are delocalized over both metal atoms on the X-band EPR time scale. The present results are compared with those of the few other V2O33+ complexes known revealing certain patterns. Crystal data for the Et(4)N[V2O3(L-alsal)(2)]. MeCN complex are as follows: chemical formula, C30H41N4O9V2; crystal system, orthorhombic; space group, P2(1)2(1)2(1); a = 9.797(5) Angstrom, b = 12.854(6) Angstrom, c = 27.550(11) Angstrom; Z = 4.